Electroacoustical transducer



Nov. 1, 1960 R. E. KIRK 2,958,740

ELECTROACOUSTICAL TRANSDUCER Filed sept. 1, 1959 l zo lgELEC'IROACOUSTICAL TRANSDUCER Roger E. Kirk, Waco, Tex., assignor to TheBaldwin Piano Company, Cincinnati, Ohio, a corporation of Ohio Filedsept. V1, 1959, ser. No. 837,455

9 claims. (c1. 179-139) This invention relates generally to microphones,and more particularly to microphones which are especially adapted forcommunication purposes in locations with high background noise.

Voice communication in areas of high background noise experiencesdifliculty in both receiving and transmitting. Most of the difficultiesin receiving in such high noise lareas are solved by means of headsetsprovided with sound shields which completely encompass the wearers ears.However, since vocal transmission generally involves sounds spoken fromthe mouth and the mouth and the nose are necessary for other bodilyfunctions, the transmission of sound cannot simply be solved by theprovision of a sound absorbent shield. If a microphone is mounted in ashield which covers the nose and mouth of the wearer as disclosed in thePatent No. 2,398,076 of Bulbuliam entitled Aviation Mask, communicationis interrupted whenever the wearer desires to eat, smoke, or perform anumber of other functions Which require removal of the mask. The mask isthus clearly inconvenient for the wearer and also tends to impair hisvision. In addition, moisture as a result of breathing tends to attackthe microphone and deleteriously affects its operation. If oxygen mustbe supplied to the wearer, as is often the case when the mask isemployed in high altitude flying, the oxygen equipment increases theweight of the mask and requires compromises in the acoustical design ofthe mask. In addition, electrical failures may result in explosion ofthe oxygen.

It is, therefore, one of the objects of the present invention to providea shielded microphone for communication in high background noise areaswhich need not be mounted in front of the mouth of the wearer but iscapable of operating as a contact microphone on some other part of thebody.

The contact microphones which have been known, such as that disclosed inPatentl No. 2,121,779 entitled Sound Translating Apparatus toBallantine, have not proven satisfactory even for use in areas of lowbackground noise because of their inability to faithfully reproducevocal sounds. It is therefore a further object of the present inventiontoprovide a contact type microphone capable of more faithfulreproduction of vocal sounds than those contact microphones which haveexisted heretofore.

It is also an object of the present invention to provide a communicationtype microphone capable ofr responding to speech within an area of highbackground noise which produces an improved signal-to background noiseratio.

The objects of this invention are achieved by providing a pressuregradient acoustical transducer mounted within a cavity in a sound oracoustical shield. Pressure gradient acoustical transducers are alsoknown to the art, as disclosed in Patent No. 2,587,684 entitledDirectional Microphone to B. Bauer, and produce a response equal to` thepressure differences on two sound tetes att` 2,958,746 Patented Nov. 1,1960 sensitive surfaces, generally the front and back surfaces of theacoustical transducer diaphragm. A microphone constructed according tothe present invention equally attenuates the -background noises at thetwo sound sensitive surfaces of the transducer, however, only one of thesound sensitive surfaces is shielded from the confronting surface of themicrophone wearer so that the microphone becomes responsive to the soundpressure exerted on the other surface of the acoustical transducer.

The invention and its utilities will be more fully appreciated from thefollowing description of a preferred embodiment of the invention whichis illustrated in the figures, in which: Y

lFigure l is a diagrammatic view of. a microphone embodying theprinciples of the present invention, the View being taken in verticalsection;

Figure 2 is a lower plan View of a microphone which constitutes apreferred embodiment of the present invention;

Figure 3 is a sectional view of the microphone of Figure 2 taken alongthe line 3-3 of Figure 2;`

Figure 4 is a sectional view of the microphone of Figures 2 and 3 takenalong the line 4--4 of Figure 2; and

Figure 5 is a top plan view of the microphone illustrated in Figures 2,3, and 4.

Figure l illustrates a pressure gradient electroacoust-ical transducer11i mounted within -a cavity 12 of a microphone casing 14. The casing 14is of sound attenuating material and may be compliant as in the case ofrubber or soft plastic, or may be a rigid body such as clay or hardplastic. The casing 14 is in contact with the skin or surface of aperson using the microphone, designated 16. This surface may be thethroat of the person, the cheek, the forehead, the temples or some otherpart of the anatomy.

The electroacoustical transducer 11i has opposite surfaces 18 and 21Bwhich are sound sensitive, and these surfaces are disposed normal to thesurface of the skin 16 of the person using the microphone. This is apreferable construction because each of the surfaces 18 and 20 willexperience sound pressures from ambient noise which have beenapproximately equally attenuated by the casing 14, however, it ispossible to obtain equal sound attenuation for ambient noises with thesurfaces 18 and 20 disposed at different angles to the surface of theskin 16. The sound responsive surface 21) is in communication with theskin 16 through a passage 22, however, the sound responsive surface 18is shielded from the skin 16 by the casing 14. A small chamber 24confronts the sound responsive surface 18 in order to approach the sameacoustical loading on the surface 18 as provided by the passage 22 forthe surface 20 of the electroacoustical transducer 11i. Straps 25 aresecured to opposite sides of the casing 14 to secure the microphone tothe body of the user.

Ambient noises will strike both the sound sensitive surfaces 18 -and 21)of the electroacoustical transducer 10 with approximately equalpressures, and since the electroacoustical transducer 1.0v responds todifferences in the sound pressures on the two surfaces, the responses ofthe two surfaces to ambient noises essentially cancel each other. Soundsproduced by the skin 16 are transmitted through the passage 22 andimpressed upon the sound sensitive surface 2@ of the transducer 10, andsince the sound sensitive surface 18 is shielded from the skin 16, thetransducer responds directly to these sounds.

The constructional details of a microphone of preferred constructionwhich operates on the principle described with reference to Figure l isshown in Figures 2 through 5; ln these figures, the microphone isillustrated with a casing 26 having an essentially semi-spherical outersurface 28 which extends from a central circular bore 30. A cone shapedrecess 32 extends into the casing symmetrically about the axis of thebore 30 and from the opposite side of the casing. A flat wall 34 extendscentrally across the recess 32, and the wall 34 is provided with acylindrical projection 36 which is snugly anchored within the bore 30 ofthe casing 26. The wall 34 divides the recess 32 into two chambers 38and 40, and a cylindrical channel or opening 42 extends through the wall34 between the two chambers 38 and 40, the opening 42 being disposed onthe axis of the bore 30 in the casing 26. A cylindricalelectroacousticaltransducer 44 is snugly mounted within the opening 42in the wall 34,.and the sound sensitive surfaces of the pressuregradient transducer 44 are designated 46 and i8 and confront the twochambers 38 and 40, respectively.

As indicated in Figure 3, the sound sensitive surface 46 is formed by adiaphragm 50, and the sound sensitive surface 48 is formed by adiaphragm 52. The diaphragms 50 and 52 are interconnected at theircenters by a coupling rod 54, and the peripheries of the diaphragms abutcoaxially mounted, hollow cylindrical magnets S6 and S8. A magneticsleeve 60 is disposed about the rod 54 and is mounted to the magnets 56and 58 by a disc shaped ange 62 extending normally from the rod anddisposed between the magnets 56 and 58. The sleeve 60 confronts and isspaced from each of the magnetic diaphragms and 52, thereby forming twomagnetic gaps, and the sleeve 65B supports serially connected coils 64and 66 wound about the sleeve 60 on opposite sides of the flange 62.This electroacoustical transducer is more thoroughly described in thepatent of Robert K. Duncan, No. 2,950,358 entitled ElectromechanicalTransducer.

A plate 68 of sound absorbent material is mounted to the end of the wall34 opposite the casing 26 and extends across the chamber 4t) to theperipheral edge of the casing 26. The plate 68 carries a layer 76 ofmaterial simulating the acoustical properties of body tissue on itssurface confronting the chamber 40.

A at, hollow, circular tube 72 is mounted to the casing 26 and plate 68to provide a suitable contact and seal with the body tissue of theperson wearing the microphone. The tube 72 has a channel 74 extendingtherethrough which is lled with a liquid 76 to form a cushion betweenthe microphone and the body tissue. Straps 78 are attached to oppositesides of the casing 26 for the purpose of securing the microphone incontact with the skin of the person employing the microphone.

When the tube 72 is disposed in contact with the body tissue of aportion of the body carrying speech energy, the speech energy entersinto the recess 32, but due to the plate 68, the speech energy issubstantially shielded from the chamber 40 while the speech energyfreely enters the chamber 38. Since the chambers 38 and 40 are shaped toform horns with the diaphragm 50 and the diaphragm 52 essentially at thethroats of the ho-rns, optimum transmission of speech energy is achievedthrough the chamber 35, and optimum acoustical coupling to the diaphragm50 is also achieved. The chambefr 40 is made as near identical to thechamber 38 as possible so that ambient noises passing thorugh the casing26 are impressed upon the diahpragm 52 in approximately the sameamplitude as they are impressed upon the diaphragm 50 Iconfronting thechamber 38. It is preferable that the portion o-f the chamberconfronting the body tissue for both chambers 38 and 40 be identical,and for this reason the layer 70 which closes the end of the chamber 4t)opposite the casing 26 is constructed of material having approximatelythe same properties as body tissue or skin. It has been found thatneoprene of the proper durometer achieves this end,

and therefore the layer 70 in a preferred construction of the microphonedescribed herein is a 1/16 inch sheet of neoprene. The plate 68mustfunction to attenuate sound, however, it must alsofoccupy a minimum ofspace in order to permit the chamber `4t! to resemble the chamber 38 asnear as possible. For this reason, an aluminum sheet is employed for theplate 68, although other materials such as brass could also beemploye-d.

The wall 314 is also constructed of neoprene and is 1/2 inch thick. Thepurpose of using neoprene for the wall 34 is to provide a cushionmounting for the elec-troacoustical transducer 44. The casing 26 isconstructed of clay, and hence is a rigid body. However, the casingcould also be constructed of a compliant material, such as polyethyleneplastic or rubber. The functions of the casing are to support theelectroacoustical transducer 44 and to attenuate impinging sound fromthe ambient atmosphere. The tube 72 is constructed of polyethyleneplastic, and theV liquid 76 is glycerine. Since the plastic of the tube72 is compliant, exerting of a pressure on one portion of the tube.results in redistribution of the liquid therein.

It is to be noted that the pressure gradient electroacousticaltransducer 44 is of a type which employs two spaced diaphragms. It is tobe understood that the invention is not limited to this type ofelectroacoustical transducer, and that the electroacoustical transducermay be any type of pressure gradient transducer. It is to be noted thatthe transducer functions as a pressure gradient transducer forbackground noises and essentially as a pressure transducer for soundsstriking the diaphragm in communication with the body tissue as a resultof the casing construction.

From the foregoing -disclosure it will be apparent to those skilled inthe art that microphones may be constructed in many differentconfigurations other than that disclosed while utilizing the teachingsof the present invention. It is therefore intended that the scope of thepresent invention be not limited by the foregoing disclosure, but ratheronly by the appended claims.

The invention claimed is:

1. A microphone suitable for use with high background noise having asound attenuating casing, and an electroacoustical transducer mountedwithin the casing, said transducer having two sound responsive surfaces,and being responsive to the sound pressure difference between the twosurfaces, characterized by the construction wherein the casing isprovided with a sound passage from the exterior thereof to one of thesound responsive surfaces of the transducer, and is provided with asound absorbent layer between the other sound responsive surface of thetransducer and all portions off the exterior surface of the casing. y

2. A microphone suitable for use with high background noise having asound attenuating hollow casing and an electroacoustical transducermounted within the casing, said transducer having two parallel soundresponsive surfaces and being responsive to the difference in soundpressure on the two surfaces characterized by the construction whereinthe casing is provided with a wall dividing the casing interior into twochambersand hav- `ing an opening therein, the transducer beingacoustically sealed within the opening with one sound sensitive surfaceconfronting each chamber, and said casing having a sound passageextending from one of the chambers tothe exterior thereof and enclosingthe other chamber.

3. A microphone suitable for use with high background noise ycomprisinga body of sound attenuating material having a recess on one side thereofextending therein from a mouth, an electroacoustic transducer having twosound responsive surfaces and being responsive to the difference insound pressures impinging on the two surfaces, said transducer beingmounted in the recess of thebody with both surfaces substantiallyequally shielded from sounds entering the recess through the body, and

means disposed between only one of the surfaces and the mouth of therecess for acoustically shielding said su-rface rom sounds enteringthrough the mouth of the recess.

4. A microphone suitable Ifor use with high backgnound noise comprisinga body of sound attenuating material having a recess on one side thereofextending therein from a mouth, a wall mounted tol the body extendingacross Ithe recess and dividing the recess into two essentially equalportions, said wall having an opening therein, an electromechanicaltransducer acoustically sealed within the opening in the wall having adiaphragm confronting each of the two portions of the recess, saidtransducer being responsive to the sound pressure difference exertedthereon from the two portions of the recess, and a sound attenuatingmember extending from the wall to the body across only one of the twoport-ions of the recess, said member acoustically shielding the oneportion of the recess from sound entering therein from the mouth of therecess.

5. A microphone `comprising the elements of claim 4 wherein the recessin the body is conical, whereby each portion of the recess forms a hornto :loa-d the confronting diaphragm.

6. A microphone comprising the elements of claim 4 wherein the soundattenuating member is provided with a surface confronting the oneportion of the recess having the acoustical properties of human skin.

7. A microphone comprising the elements of claim 4 wherein the soundattenuating member is provided with a layer of neoprene confronting theone portion of the recess.

8. A microphone suitable for use with high background noise comprisingthe elements of claim 3 in combination with an endless hollow tubesealed and mounted to the casing about the month thereof, said tubebeing constructed of compliant material and having a liquid on theinterior thereof.

9. A contact type microphone suitable for use with high background noisecomprising, in combination, a semispherical solid body of soundattenuating material having a radial bore extending therethrough at itscenter and a conical recess extending therein from the side opposite thespherical surface coaxially with the bore, a neoprene wall mountedwithin the recess onI the axis thereof dividing the recess -into twoequal port-ions, said wall having a cylindrical projection sealed withinthe bore of the casing and an opening extending therethroughtransversely intersecting the axis of the bore of the casing, anelectromechanical transducer acoustically sealed within the openinghaving a pair of diaphragms confronting the two portions of the recess,said transducer being electrically responsive to the diierence in soundpressure on the two diaphragme a plate sealed to lthe end of the wallopposite the casing and to the portion of the casing adjacent to the`one portion of the recess on one side of the wall, a layer of neoprenedisposed on the plate confronting the one portion of the recess, and acircular hollow liquid lled tube of compliant material sealed to thecasing about the recess.

No references cited.

